ROYAL Bank of Scotland has ranked bottom for customer satisfaction out of nearly 20 rivals for the second-year running.

Research by consumer body Which? has found that the taxpayer-owned bank scored particularly badly when it came to transparency charges and penalties.

More than 5,000 customers were surveyed about their bank's complaints procedure, clarity of charges and penalties, as well as the accessibility of online and mobile banking among others.

Topping the satisfaction list was First Direct followed by Nationwide and TSB Bank. Clydesdale Bank - the best rated Scotland-based operation - came fourth.

RBS, the worst performer according to the survey, scored an overall customer score of 54 per cent, with HSBC given a score of 56 per cent and NatWest a score of 57 per cent. First Direct regularly tops customer satisfaction surveys, but Which? said it "may not be for everyone" as it does not have physical branches.

Which? found fees and charges are still a "mystery" to many customers, with no provider in the survey given a maximum score.

The consumer group has a campaign called "stop sneaky fees and charges," which urges financial firms to put an end to hidden and hard-to-compare costs.

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The research also suggested that banks' mobile and online services are improving, with several major providers receiving maximum scores on this aspect of their service.

Vickie Sheriff, Which? director of campaigns and communications, said: "Day-to-day banking is an essential part of life and dealing with your bank should be simple and straightforward.

"While there are positive signs in some areas, such as online and mobile banking, banks have a long way to go in making their prices clear to stop people being hit with unexpected charges. If the banks aren't doing enough to ensure their penalty fees are fair, it is right that the regulator should step in."

While RBS's rating was rated equal worst for the charges transparency, value, customer service, communication and its telephone banking service, the bank has continued to be dogged by technical glitches.

In October, customers reported having their debit cards declined in shops and at ATMs. It came a fortnight after Andrew Tyrie, chairman of the Commons Treasury select committee, spoke out about bank IT system failures and the impact they were having on customers.

On New Year’s Day last year debit card holders reported having their cards declined at tills and their pins blocked.

While in September 2015, NatWest and RBS customers were hit by a technical problem that meant some could not withdraw cash or use their card in branches.

The previous year it was hit with a £56 million fine from the Bank of England and City watchdog Financial Conduct Authority after a computer failure in 2012 saw as many as 6.5 million customers unable to make payments for as long as three weeks.

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An RBS spokesman said: "We are committed to serving our customers and providing them with the best possible service.

"Our award-winning mobile app is helping millions of customers to bank on the move and is highly rated by our customers and by the Which? research."

A recent investigation by the Competition and Markets Authority (CMA) suggested customers often under-estimate how heavily they rely on their overdrafts and complex overdraft charging structures can make it hard to work out whether they could be better off elsewhere.

The Financial Conduct Authority (FCA) is putting overdrafts under the spotlight as part of a probe into the high-cost credit market.

A spokeswoman for the British Bankers' Association (BBA) said: "Banks compete to attract and retain customers every day. They are also focused on giving their customers the best outcome for the services they provide and have invested heavily in digital technology to alert customers when their account might be slipping into the red to help them to avoid unnecessary fees and charges.

"As part of the CMA review of the retail banking market, banks will continue to work with the FCA to test what more could be done to enhance clarity on fees and charges and implement alerts and prompts to increase customers' awareness of their overdraft.

"The level of overdraft charges has fallen dramatically, with customers saving nearly £1 billion a year and a number of products now offering fee and interest free facilities within an approved overdraft limit. If you think that you might need to borrow money, speak to your bank to pre-arrange an overdraft facility to be certain that payments will be made and keep borrowing costs down."